The goal of this research is to understand the system by which people internally represent the locations of objects and the spatial relationships among them. It is hypothesized that this system involves an analogue model of the external world, as well as various facilities for digital or symbolic representation; this hypothesis is supported by some of the results already obtained under the present project. Work on the representation of the world behind the head, and its coordination with the perceived world in front, will be continued. The major portion of the proposed research, however, will develop and utilize a family of mental tasks involving the transformation and combination of vectors, which we believe will tap some of the most crucial processes of spatial representation. These vector tasks should enable us to discriminate between analogue and symbolic processes in some cases, to study visual imagery in a more quantitative way than has hitherto been possible, and to investigate anchoring effects of visual stimulus configurations on imaginal constructs.